Research Papers

Numerical Investigation on the Performance of a Regenerative Flow Turbine for Small-Scale Organic Rankine Cycle Systems

[+] Author and Article Information
Ramin Moradi

Dipartimento di Ingegneria Astronautica,
Elettrica ed Energetica,
Sapienza Università di Roma,
Via Eudossiana 18,
Rome 00184, Italy
e-mail: ramin.moradi@uniroma1.it

Luca Cioccolanti

Centro di Ricerca su Energia, Ambiente e
Università Telematica eCampus,
Via Isimbardi 10,
Novedrate, CO 22060, Italy
e-mail: luca.cioccolanti@uniecampus.it

Enrico Bocci

Dipartimento di Fisica Nucleare, Subnucleare e
delle Radiazioni,
Marconi University,
Via Paolo Emilio 29,
Rome 00193, Italy
e-mail: e.bocci@unimarconi.it

Mauro Villarini

Dipartimento di Scienze Agrarie e Forestali,
Tuscia University of Viterbo,
San Camillo de Lellis, snc, Viterbo 01100, Italy
e-mail: mauro.villarini@unitus.it

Massimiliano Renzi

Facoltà di Scienze e Tecnologie,
Libera Università di Bolzano,
Piazza Università 5, Bolzano, BZ 39100, Italy
e-mail: Massimiliano.Renzi@unibz.it

1Corresponding author.

Manuscript received January 16, 2019; final manuscript received June 13, 2019; published online July 11, 2019. Assoc. Editor: Sunil Patil.

J. Eng. Gas Turbines Power 141(9), 091014 (Jul 11, 2019) (9 pages) Paper No: GTP-19-1015; doi: 10.1115/1.4044062 History: Received January 16, 2019; Revised June 13, 2019

In this study, the performance characteristics of a regenerative flow turbine (RFT) prototype have been investigated by means of a computational fluid dynamics (CFD) study. The prototype has been initially designed to be used in gas pipelines replacing expansion valves but, because of the intrinsic characteristics of this kind of expander, its use can be extended to other applications like the expansion process in small-scale organic Rankine cycle (ORC) plants. In the first part of this work, the numerical results of the CFD analysis have been validated with the experimental data reported in literature for the same turbine prototype. After the validation of the model, a detailed study has been carried out in order to evaluate specific features of the turbine, focusing the attention on the typical operating conditions of small-scale low-temperature ORC systems. Results have shown that the considered RFT prototype operates with higher isentropic efficiencies (about 32% at 6000 rpm) at lower mass flow rates, while the power output is penalized compared to other operating points. The numerical analysis has also pointed out the high impact of the losses in the leakage flow in the gap between the blade tips and the stripper walls. Therefore, the CFD analysis carried out has provided a thoughtful understanding of the performance of the expander at varying operating conditions and useful insights for the future redesign of this kind of machine for the application in small-scale ORCs.

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Fig. 1

RFT and impeller: experimental apparatus (a) and (b) [17] and three-dimensional model (c) and (d)

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Fig. 2

Half-section view of the RFT with dimensions

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Fig. 3

Three-dimensional mesh domain of the RFT with zoom-in mesh structure of the leakage gap zone

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Fig. 4

Variation of the outlet temperature with mesh density

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Fig. 5

Comparison of outlet temperature (top) and isentropic efficiency (bottom) between CFD results and experimental data [17]

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Fig. 6

Velocity vectors in a typical cross section plane in the channel at 3000 rpm (BM = 0.08) and 0.3 kg/s (m˙=0.054)

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Fig. 7

Iso-pressure surfaces at 3000 rpm (BM = 0.08) and 0.3 kg/s (m˙=0.054)

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Fig. 8

(a) position of sample points along the channel and (b) variations of total pressure along the channel at 3000 rpm (BM = 0.08) and different flow rates

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Fig. 9

The total pressure ratio of the RFT at different working conditions

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Fig. 10

Streamlines colored by the total temperature of the flow at 6000 rpm (BM = 0.16) and 0.2 kg/s (m˙=0.038)

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Fig. 11

Isentropic efficiency by reduced mass flow rate in different BMs

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Fig. 12

Power coefficient (ψ) by reduced mass flow rate in different BMs

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Fig. 13

Relative entropy loss coefficient in three zones at 3000 rpm (BM = 0.079) and 0.3 kg/s (m˙=0.054)



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